The present invention relates to a rotation detector, and more particularly, to a rotation detector that includes a magnetic sensing element.
The applicant has proposed a rotation detector, or a rotation position sensor 51, as illustrated in FIG. 15. The rotation position sensor 51 has an iron rotating plate 52 and a sensor body 53. The rotating plate 52, which is in the shape of disk, is secured to a steering shaft 54 of a vehicle. The rotating plate 52 rotates together with the steering shaft 54 about the axis of the steering shaft. Extending from the peripheral edge of one surface of the rotating plate 52, a plurality of arcuate iron magnetic path changing pieces 55 are formed. Each piece 55 is coaxial with the shaft 54.
The sensor body 53 is located outside of and close to the magnetic path changing pieces 55. The sensor body 53 includes a plurality of magnetic sensing bodies 56 encapsulated by a resin molding material 57 and fixed to a fixing member, not shown. Each of the magnetic sensing bodies 56 includes a bias magnet 56b, which is opposite to the rotating plate 52 and oriented in a predetermined direction, and a magneto-resistive element 56a, which detects magnetic flux of the bias magnet 56b. The direction of the magnetic flux of each bias magnet 56b is changed when the associated magnetic path changing piece 55 passes a position corresponding to the magnetic sensing body 56 as the rotating plate 52 is rotated. The magneto-resistive element 56a detects changes in the direction of the magnetic flux of the associated bias magnet 56b. In this way, rotation is detected.
In the rotary position sensor 51 thus formed, however, if a disturbance source G such as a coil exists nearby, as indicated by broken lines in FIG. 15, disturbance magnetic flux m may be generated from the disturbance source G. Thus, when detecting the presence or absence of a magnetic path changing piece 55 between the bias magnet 56b and the axis of the shaft 54, the disturbance magnetic flux m may affect the rotating plate 52 and the magnetic path changing piece 55 and adversely affect the magnetic sensing bodies 56.
Specifically, even though a magnetic path changing piece 55 is located between the bias magnet 56b and the axis, the associated magneto-resistive element 56a may detect magnetic flux having a direction substantially similar to that of the flux in existence when the magnetic path changing piece 55 is not between the bias magnet 56b and the axis. Conversely, the magneto-resistive element 56a may detect magnetic flux having a direction substantially similar to that of the flux in existence when the associated magnetic path changing piece 55 is between the bias magnet 56b and the axis although the magnetic path changing piece 55 is not between the bias magnet 56b and the axis.
Accordingly, it is an objective of the present invention to provide a rotation detector that is capable of eliminating the influence of disturbance on magnetic sensing of a magnetic sensing element even if a disturbance source is positioned near the rotation detector.
In order to achieve this object, in accordance with the present invention, there is provided a rotation detector comprising: a circular rotating member; magnetic path changing pieces formed at predetermined intervals in a circumferential direction of the rotating member, each of the magnetic path changing pieces being made of a magnetic material; a magnetic sensing element for detecting magnetic flux of a magnet located in a predetermined orientation to the rotating member; and a shielding member covering at least a portion of the magnet and the magnetic sensing element, wherein the shielding member is made of a magnetic material.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.